STRENGTH TESTS OF STRUCTURAL TIMBERS. 



average strength at elastic limit and stiffness. In the air-seasoned 

 beams the untreated butt cuts were higher in strength and stiffness 

 than the treated top cuts, but, on the other hand, the untreated top 

 cuts fell below the treated butts in strength and stiffness in nearly 

 every case. In the partially seasoned stringers the treated and 

 untreated material falls together somewhat more closely. 



7es+ed D/'rect/y after 7reafaierrf- 



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3 - Butts T = Tops 



Fig. 3.— Effect of preservative treatment on the strength and stiffness of loblolly-pine stringers treated 



partially air dry. 



DOUGLAS FIR. 



Figures 5 and 6 show the strength and stiffness of treated and 

 untreated stringers of green and seasoned Douglas fir, respectively, 

 treated by the so-called " boiling ;J process as used in this case. There 

 appears to be a marked weakening of the breaking strength with the 

 particular treatment used. The average breaking strength of the 

 stringers tested green and after seasoning is 33 per cent and 39 per 

 cent, respectively, less than the average strength of the natural 

 stringers. The fiber stress at elastic limit also appears to be reduced, 

 although to a somewhat less extent. In the green material no 

 weakening is apparent in the stiffness. The seasoned stringers, 

 however, show a falling off in stiffness in the treated material. 



Figure 7 shows the strength and stiffness of green * Douglas fir 

 treated by the so-called "steaming" process. The breaking strength 



1 The air-seasoned material is not yet tested, July, 1915. 



